1. Field of the Invention
This invention relates generally to a semiconductor technique and more particularly to a silicone polymer insulation film on a semiconductor substrate and a method for forming the film by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of the Related Art
Because of the recent rise in requirements for the large-scale integration of semiconductor devices, a multi-layered wiring technique attracts a great deal of attention. In these multi-layered structures, however, capacitance among individual wires hinders high speed operations. In order to reduce the capacitance it is necessary to reduce relative dielectric constant of the insulation film. Thus, various materials having a relatively low relative dielectric constant have been developed for insulation films.
Conventional silicon oxide films SiOx are produced by a method in which oxygen O2 or nitrogen oxide N2O is added as an oxidizing agent to a silicon material gas such as SiH4 or Si(OC2H5)4 and then processed by heat or plasma energy. Its relative dielectric constant is about 4.0.
Alternatively, a fluorinated amorphous carbon film has been produced from CxFyHz as a material gas by a plasma CVD method. Its relative dielectric constant ε is as low as 2.0-2.4.
Another method to reduce the relative dielectric constant of insulation film has been made by using the good stability of Si—O bond. A silicon-containing organic film is produced from a material gas under low pressure (1 Torr) by the plasma CVD method. The material gas is made from P-TMOS (phenyl trimethoxysilane, formula 1), which is a compound of benzene and silicon, vaporized by a babbling method. The relative dielectric constant ε of this film is as low as 3.1. 
A further method uses a porous structure made in the film. An insulation film is produced from an inorganic SOG material by a spin-coat method. The relative dielectric constant ε of the film is as low as 2.3.
However, the above noted approaches have various disadvantages as described below.
First, the fluorinated amorphous carbon film has lower thermal stability (370° C.), poor adhesion with silicon-containing materials and also lower mechanical strength. The lower thermal stability leads to damage under high temperatures such as over 400° C. Poor adhesion may cause the film to peel off easily. Further, the lower mechanical strength can jeopardize wiring materials.
Oligomers that are polymerized using P-TMOS molecules do not form a linear structure in the vapor phase, such as a siloxane structure, because the P-TMOS molecule has three O—CH3 bonds. The oligomers having no linear structure cannot form a porous structure on a Si substrate, i.e., the density of the deposited film cannot be reduced. As a result, the relative dielectric constant of the film cannot be reduced to a desired degree.
In this regard, the babbling method means a method wherein vapor of a liquid material, which is obtained by having a carrier gas such as argon gas pass through the material, is introduced into a reaction chamber with the carrier gas. This method generally requires a large amount of a carrier gas in order to cause the material gas to flow. As a result, the material gas cannot stay in the reaction chamber for a sufficient length of time to cause polymerization in a vapor phase.
Further, the SOG insulation film of the spin-coat method has a problem in that the material cannot be applied onto the silicon substrate evenly and another problem in which a cure system after the coating process is costly.
It is, therefore, a principal object of this invention to provide an improved insulation film and a method for forming it.
It is another object of this invention to provide an insulation film that has a low relative dielectric constant, high thermal stability, high humidity-resistance and high adhesive strength, and a method for forming it.
It is a further object of this invention to provide a material for forming an insulation film that has a low relative dielectric constant, high thermal stability, high humidity-resistance and high adhesive strength.
It is a still further object of this invention to provide a method for easily forming an insulation film that has a low relative dielectric constant without requiring an expensive device.